We are continuing our studies of gene expression in rat liver cells with an emphasis on alphafetoprotein and albumin gene activity. In part, the rationale for these studies resides in the availability of sensitive assays for monitoring the expression of AFP and ALB genes during times such as fetal and neonatal development, liver regeneration, tumor growth and carcinogenesis when fundamental alterations in mechanisms of gene expression might reasonably be expected to occur. Analysis and interpretation of quantitative, as well as qualitative, changes in the level of gene expression and a description of the methods used to regulate this expression are goals of our studies. Towards these ends we have developed assays for the transcriptional and translational activity of AFP and ALB genes and applied them to the study of gene expression in several biological systems of interest. We are presently focusing our studies on: (1)\defining the involvement of methylation of AFP and ALB structural genes or regulatory elements on transcriptional activity by examining restriction endonuclease digests of genomic DNA, by assessing DN'ase I sensitivity of the AFP and ALB genes during, for example, normal liver development and hepatocellular carcinogenesis and also by documenting the effect of azacytidine on the expression of AFP and ALB in cultured fetal and adult hepatocytes; (2)\on refining methods to identify AFP mRNA synthesizing putative preneoplastic cell populations in hepatocarcinogen treated rats using in situ hybridization techniques; and (3)\to initiate studies using DNA transfection techniques to determine if there is a transforming gene in rat hepatomas and at what time and in what cell type(s) it appears during hepatocarcinogenesis.